1. Field of the Invention
The present invention relates to a proximity detection device for detecting an approach and a position of an object by a human finger or the like by changes in electrostatic capacitances of respective intersections of plural electrodes arranged in correspondence with two-dimensional coordinates.
2. Description of the Related Art
It is known that, when an object of a human finger or the like approaches between two closely located electrodes, the electrostatic capacitance between the electrodes changes. Proximity detection devices such as an electrostatic touch sensor to which the principle is applied to the detection of the electrostatic capacitances of respective intersections of plural electrodes arranged in correspondence with two-dimensional coordinates in a detection area have been disclosed, and some of them have been put into practical use (for example, see JP-T-2003-526831).
An example of the conventional proximity detection device will be explained based on FIG. 8.
In the example of FIG. 8, in a detection area 2 of a supporting unit 1, transmitting electrodes 3 corresponding to longitudinal coordinates and receiving electrodes 4 corresponding to lateral coordinates are arranged orthogonally to each other. To the transmitting electrodes 3, a periodic alternating voltage is line-sequentially applied with respect to each electrode from a line-sequential driving unit 35. The alternating voltage is transmitted to the receiving electrode 4 by the electrostatic coupling of the intersection between the transmitting electrode 3 and the receiving electrode 4. In a current measurement unit 6, values corresponding to the electrostatic couplings of the respective corresponding intersections from currents flowing in the virtually grounded receiving electrodes 4 are detected, and the detected values are output to a proximity computing unit 8. Here, in order to accumulate and obtain weak alternating currents, accumulation capacitors have been switched in synchronization with periodic alternating voltages sequentially and selectively applied to the transmitting electrodes 3 or the currents have been accumulated by convolving demodulated waveforms.
However, in the case of the example shown in FIG. 8, detection efficiency has been problematic because of line-sequential driving. To solve the problem, a multiline-driven proximity detection device as shown in FIG. 2 has been disclosed. In the example of FIG. 2, the transmitting electrodes 3 corresponding to the longitudinal coordinates and the receiving electrodes 4 corresponding to the lateral coordinates are arranged orthogonally to each other in the detection area 2 of the supporting unit 1. To the transmitting electrodes 3, different patterned waveforms are simultaneously applied to the plural transmitting electrodes 3 from a multiline driving unit 5. The waveform is transmitted to the receiving electrode 4 by the electrostatic coupling of the intersection between the transmitting electrode 3 and the receiving electrode 4. In a current measurement unit 6, currents flowing into the virtually grounded receiving electrodes 4 are measured.
Here, a computing unit 10b includes a correlation computing unit 17 and a proximity computing unit 8, obtains electrostatic capacitances of intersections between the respective transmitting electrodes and receiving electrodes 4 or their changes from correlations between the patterns applied to the transmitting electrodes 3 and the measurement values of the current measurement unit 6 in the correlation computing unit 17, and computes the position of the approaching object by weighted average or the like in the proximity computing unit 8 (for example, see JP-A-9-292950).
Further, a method for effective detection with significantly increased number of times of charging and discharging by modulating and driving carriers according to the patterns applied to the transmitting electrodes 3, has been disclosed (for example, see JP-T-2009-516295).
In the above described conventional proximity device using multiline driving, there have been problems that the amount of computation in the correlation computing unit is large and a high-speed computer is necessary for higher detection speed. Further, in the case where the patterns applied to the transmitting electrodes are not completely orthogonal, there has been a problem that crosstalk occurs in the correlation computation result.
Accordingly, in the invention, in order to solve the problems in the conventional art, a device and method as described below are provided.
That is, there are provided a device and method, even in the case where the patterns applied to the transmitting electrodes are not completely orthogonal, that can obtain values in response to the electrostatic capacitances of the respective intersections of the detection panel without crosstalk by treating the patterns applied to the transmitting electrodes and characteristics of a detection panel as matrices and multiplying the measurement values of the current measurement unit by an inverse matrix of the patterns applied to the transmitting electrodes.
Further, there are provided a device and method that can perform detection at a high speed detection without using a high-speed computer by providing a memory unit that stores an interim result of the computation of  using an inverse matrix and using patterns applied to the transmitting electrodes for enabling faster computation through the utilization of the memory unit.